Technical Abstract:
Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) adults were collected from a whitefly colony maintained on hibiscus plants, weighed and stored at -80 C. Groups of adults (30-50 mg) were placed into a 20-ml glass vial containing 8-10 ml of CHCl3/methanol (2:1) and covered with a Teflon-lined cap. To homogenize (sonicate) the tissues, the vial was placed in the water bath of a Fisher Scientific, Model FS 60, ultrasonic cleaner for 15-30 min. The homogenate was filtered through glass wool with CHCl3 and the CHCl3 washed with water. The lipid extract in CHCl3 was spotted on 250- m silica gel TLC plates and the triacylglycerol (TAG) fraction was separated from other lipid fractions by developing the TLC plates in hexane/ethyl ether/formic acid (80:20:1). The purified TAG fraction was visualized with iodine vapors, scraped from the TLC plates and eluted from the silica gel with CHCl3.
High performance liquid chromatography (HPLC) was used to separate the TLC-purified mixture of TAG using a ChromSpher 5 Lipid column (Chrompack, 5 m, 4.6 X 250 mm). Mass detection of TAG constituents was performed using a Sedex (Model 55) evaporative light scattering detector (ELSD). Peak areas from the ELSD were used to determine quantities of resolved TAG components and structural identifications were made by HPLC-MS. Individual TAG components were identified by comparing their column retention times to those of authentic TAG standards and by comparative mass spectral analysis using the Waters Model 2690 Separations Module linked to a Waters Thermabeam Mass Detector.
For the mixture of triacylglycerols from B. argentifolii adults, the major fatty acid constituents were identified as oleic acid (18:1), palmitic acid (16:0), stearic acid (18:0) and linoleic acid (18:2), in descending order of abundance. Lesser amounts of palmitoleic acid (16:1) and arachidonic acid (20:0) were detected, as well as trace amounts of myristic acid (14:0). The major intact TAG in decreasing order of abundance, as analyzed by HPLC-MS, were 1-palmitoyl-2,3-dioleolylglycerol (POO), 1,2-dipalmitoyl-3-oleoylglycerol (PPO),
1-palmitoyl-2-stearoyl-3-oleoylglycerol (PSO), 1,2,3-trioleoylglycerol (OOO), 1-stearoyl-2,3-dioleoylglycerol (SOO), 1-palmitoyl-2-oleoyl-3-linoleoylglycerol (POL) and 1-palmitoyl-2-linoleoyl-3-stearoylglycerol (PLS). The fatty acids of the TAG from B. argentifolii adults were also analyzed as their methyl ester derivatives following hydrolysis with 5% KOH in methanol and subsequent reaction of the free fatty acids with 10% HCl in methanol to form methyl esters. The distribution of fatty acids was similar to that indicated above for intact TAG: approximately 58% as 18:1, 29% as 16:0, and lesser amounts of 18:0, 18:2, 18:3 and 16:1. These methods developed for characterization of TAG from adults will be used to determine the TAG composition of B. argentifolii nymphs and to provide useful information in regard to the lipid nutrient reward for whitefly predators and parasitoids.